γ-P4S3I2: a new metal-free infrared second-order nonlinear optical crystal designed by polymorphism strategy

A non-centrosymmetric metal-free thiophosphate, γ-P4S3I2, was successfully synthesized utilizing polymorphism strategy in this study. γ-P4S3I2 crystallized in the space group of P43 and featured paralleled (P4S3I2)n molecular clusters. Importantly, it exhibited promising nonlinear optical (NLO) performances, such as a phase-matchable second harmonic generation (SHG) efficiency (0.5 × AgGaS2), wide band gap (2.38 eV), large birefringence (0.118@2050 nm), and wide infrared transparency, suggesting that γ-P4S3I2 may be a potential IR NLO candidate.